Tuesday, January 3, 2017

"10 Things You Should Know" with snow in the forecast

Several thoughts as another "2016-'17 Winter Season" #ArcticFront comes barreling our way.

1. Fortunately, severe weather didn't materialize in our area on Monday. Plenty of thunder (even thunderfog, which is almost as cool as thundersnow), but no high wind or hail. I'm good with that. I root for people, not storms, despite trying to produce a good forecast that sometimes includes them. Folks near the Gulf Coast weren't so lucky, including Gulf Shores.


2. At the end of the day, as the back edge of the afternoon rain shield moved across the metro, the setting sun produced some spectacular skyscapes. Some folks were treated to brilliant double rainbows, others to an awe-inspiring orange sky. Scroll through our Twitter feed for a bunch of cool photos you nice folks sent, like the one below!
3. Looking ahead, the Arctic front arrives early this evening. You'll notice the wind shift to the north and pick up pretty good if you're out. If you're out later, you'll notice it'll be a lot cooler than it's been in a few days. By morning, we'll be in the mid 30s with wind chills in the 20s. Bundle the kids up as they head to school! We could see a few stray showers with the frontal passage late this afternoon into early evening. They'll be relatively minor compared to rains of the recent past!

4. Very cold air hangs around for several days as the high pressure of Arctic origin makes its way across the northern U.S. We'll be on the south side of it, but it'll still be plenty cold. Expect lows in the 20s and highs in the 30s starting Thursday morning and continuing into early next week!

Low temperatures Sunday morning according to this morning's GFS computer model. Yes, the freezing line is as far south as central Florida with below freezing temperatures across the vast majority of the CONUS. (WxBell)

5. The million dollar question, and one that everyone wants to know the answer to, is will it snow and if so when and how much?? The latter part of that question seems to have taken on a life of its own given recent rumblings of "snowmaggedon-like" snow totals in the south from some folks who would rather share model hype rather than be responsible.

5a. BTW - we don't recommend getting your weather information from sports talk figures (I'm looking at you Clay Travis), just like you don't want my analysis of Grizzlies trade rumors. Neither of us knows what we're talking about. Stick to the experts who have skin in the game and have proven responsible in the past, and aren't out just for ratings or social media numbers!

6. The REAL answer is: I'm not exactly sure yet.  "But Erik, that's not the answer I wanted to hear!" I know, but it's the responsible answer at this point in time. I DO think there's a decent chance most of us could see some snowflakes. But I don't know exactly when and I don't know how much. YET. Maybe you've heard about how hard it is to forecast winter weather in the south (in particular)? Below are a couple of visuals to help you understand. Then I'll give you my first educated guess, since you asked...

7. First are the snowfall maps (all valid through 6pm Saturday) from the last 12 runs (4 per day) of the American-made Global Forecast System (GFS) model. Greys are light snow, blues are snowman builders, pinks are snowmaggedon. Notice how the snow starts to our north, drops the hammer right over us, then backs off again and sinks south.The last frame is from this morning's model run.


We also have this graphic which shows run-to-run consistency (or not) for the GFS model. Each row represents a run of the model. Exactly three of the last 15 models runs (or roughly four days worth) has produced more than 2" of snow.

8. But that's the American model... the Europeans are far superior, right??  I give you the European model (credit Weather Bell Analytics), same parameter, run twice a day. This is from model runs of the past 6 days:

Oh yeah...FAR superior! Haha! I will give it this though - the past couple of days it has been somewhat consistent. But it still varies from a dusting to about 2" here in the metro over that time as you can tell from the graphic below. Again, multiple (the last 11 to be exact) runs of the European model. Only one has forecast more than 2".


9. All that said, here's my best guess at the possibilities, with all the caveats applied and with medium-low confidence. Thursday night has a chance for some flurries or maybe a dusting (meaning less than 1/4"). I don't think it's the time period of greatest concern, as far as traffic problems, etc. During the day Friday, there's a better chance we could see some minor accumulation - I'm talking about maybe an inch on average. It'll be very cold and cloudy so it wouldn't go anywhere right away. An inch could be enough to possibly cause some slippery roads, especially those elevated ones we keep building, but it's not enough to even cover the grass. If I end up conservative, we could get 2 inches - but that's my upper bound right now. Flurries could linger Friday night into early Saturday, but that's also a low probability.


10. Should you get all worked up or start changing plans? No. Will schools be closed?? I have no idea. Just stay tuned. Listen to trusted sources who have proven their mettle in the past. We'll keep you sane and provide the "real deal," not the wish-cast. As the event gets closer, especially tomorrow into Thursday, we'll get more model data that is higher resolution within the forecast window of concern and things will hopefully start to become a little clearer. But remember, it's the south. It's snow. Those things don't mix, and that applies as much to forecasting it as it does to driving in it! Keep an eye on our social media feeds listed below for the latest. And if all else fails, "if it looks too good to be true, it probably is!" Don't share it.

Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Sunday, January 1, 2017

Roller coaster weather continues with strong storms then Arctic cold

Greetings to all and Happy New Year from MWN! First a word of thanks to all who supported us with your visits, questions and comments, app downloads, and calendar purchases in 2016! We had a great year and look forward to more of the same in 2017!


Speaking of more of the same... we've been on a roller coaster of ups and downs in the weather the past few weeks and the trend continues into the first week of the new year, beginning with a warm and stormy Monday, then another blast of Arctic air by mid/late week. Today's blog focuses on Monday and ends with a few comments on the cold that is coming.

A seasonal, but moisture-laden airmass is in place across the Mid-South today as a warm front sits across the central Gulf Coast states, well to our south. Meanwhile, well to the west, low pressure is moving into west TX and will shift across TX overnight to near Dallas by Monday morning, then zip east-northeast to a position very near Memphis by 6pm Monday. As the low moves toward the Mid-South, it will pull that warm front that is south of us northward, extending east from the low.

Low pressure just west of Dallas, TX early Monday morning will move along the warm front during the day as that front lifts slowly north into the area. (NOAA/WPC)

By 6pm Monday, the low will be very near Memphis with the warm front in far northern MS. The track of the low will determine the severe weather threat level for the Memphis area. (NOAA/WPC)
Scattered showers will be possible by early Monday morning with additional showers popping up as the warm front moves north and wind in the lower levels increases. By lunchtime to early afternoon, lift from the approaching warm front and low pressure system will result in showers becoming scattered thunderstorms. The threat of thunderstorms will continue until early evening when the low passes by to our east.

As far as severe weather is concerned, there is a risk of some storms being strong to potentially severe in the metro. The current Storm Prediction Center outlook for Monday indicates a Slight Risk (category 2 of 5) of severe weather roughly south of I-40 and a Marginal (category 1 of 5) north of the interstate. This outlook will be updated again multiple times tomorrow and could change slightly. The highest risk (Enhanced, category 3) is currently well south of the Memphis metro.

The highest chance of severe weather is well south of the Memphis metro, but a slight risk extends north to near the I-40 corridor in the Memphis area. A closer view is provided below. (NOAA/SPC)
There is still some uncertainty in the exact risk level due to forecast models not completely agreeing on the track of the low pressure referenced above. If it passes north of Memphis (such as suggested by the highest-resolution experimental NAM3 model), the warm front also makes it to our north and our severe weather chances increase. If it goes by a bit further to our south (as the GFS model believes it will do), severe weather chances will be lower. I am currently taking the middle road, which is most like the European model, but also supported by the high-resolution operational NAM4 model. In this scenario, we'll see a threat of severe storms in the metro during the mid to late afternoon hours, particularly over north MS, with a higher chance to our south.

The main threats with any severe storm will be damaging straight-line wind of more than 60 mph. We could also see some hail and an isolated tornado is not out of the question, but is a low risk. In addition, fueled by dewpoints rising to near 60 degrees, storms will be capable of producing very heavy rain (over 1"/hour rates) that could lead to minor flash flooding, especially if they move over the same areas repeatedly. The graphic below summarizes the timing and threats as of late Sunday afternoon.


Review the safety tips below in case severe weather occurs. As always, we highly recommend you put the MemphisWeather.net app on your smartphone and add StormWatch+ to the app to receive alerts for any severe weather watches or warnings as soon as they are issued. Links are provided below for more information or to download the app.


Looking ahead, Tuesday will be the last "pre-Arctic front" day this week as temperatures rebound into the lower 60s with just slight rain chances. By Tuesday night, that front moves through, switches wind to the north and causes temperatures to fall. The core of the cold air likely doesn't arrive until Thursday or Friday as the Arctic high builds in, but we'll be seeing temperatures that are in the 20s and 30s both days.

The NAM model forecasts temperatures near freezing at 6pm Wednesday as Arctic high pressure begins building into the region from the north. (PivotalWx)
 The previously-discussed southern stream system that had some winter weather potential is not completely ruled out, but chances of light snow are only about 20% as the coldest air moves overhead. Unfortunately, with the high building in, it will likely mean the best moisture also stays to our south, minimizing the threat of any accumulating snow. You can stay updated with the longer-range forecast via the app or at the links below to MWN and MWN Mobile.


Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook, Twitter, and Google+
Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder